Objective lens for endoscopes

Abstract

The inventive objective lens for endoscopes has independently a zooming function and a focusing function, and is capable of magnified viewing. The objective lens has an angle of view (2ω) of 100° or greater, and comprises a positive first group G1, a negative second group G2 and a positive third group G3. The third group G3 comprises a positive first (3-1) subgroup G31 and a positive second (3-2) subgroup G32. A subgroup in at least the second group G2 moves to (1) bring about a change in the focal length of the whole system and (2) correct an image position for movement in association with a focal length change, and one subgroup in the second group G2 and the third group G3 moves to the image side from a longer side toward a shorter side of the working distance (WD) to (3) correct the focal position for movement in association with a working distance change.

1. A zoom objective lens for endoscopes, characterized by having an angle of view (2ω) of 100° or greater at a wide-angle end, and comprising, in order from an object side thereof, a positive first group, a negative second group and a positive third lens group, wherein:
 said third group comprises a positive first (3-1) subgroup and a positive second (3-2) subgroup, 
 the second group comprises subgroups, wherein a lens subgroup in at least said second group moves to (1) bring about a change in a focal length of a whole system and (2) correct an image position for movement in association with a focal length change, and 
 one subgroup in said second group and said third group moves to an image side from a longer working distance (WD) side being a far end toward a shorter working distance side being a near end to correct a focal position for movement in association with a working distance change, and wherein said zoom objective lens for endoscopes satisfies the following conditions:
   0.4<( D 12 t−D 12 w )/ fw≦ 1.077  (1)′
 
   0.02<Δ Dwd/fw< 0.4  (2)
 
   0<( rb+ra )/( rb−ra )<2  (3)
 
   −0.7<1/β wd< 0.2  (4)
 
 
 
       where fw is a focal length of a whole system at the wide-angle end, a figure being obtained in a far end-defining working distance;
 D 12   w  is a spacing between the first group and the second group at the wide-angle end; 
 D 12   t  is a spacing between the first group and the second group at a telephoto end; 
 ΔDwd is an amount of movement of a moving group upon changing of the working distance from a far end to a near end, provided that a plus sign is indicative of a direction of movement of the moving group to an image side; 
 ra is a radius of curvature of an image-side surface of a first lens in the first group; 
 rb is s radius of curvature of an object-side surface of a second lens in the first group; and 
 βwd is an imaging magnification of the moving group upon a working distance change, a figure being obtained at the wide-angle end in a far end-defining working distance. 
 
     
     
       2. A zoom objective lens for endoscopes, characterized by having an angle of view (2ω) of 100° or greater at a wide-angle end, and comprising, in order from an object side thereof, a positive first group, a negative second group and a positive third lens group, wherein:
 the second group has an aperture stop, 
 the third group comprises a positive first (3-1) subgroup and a positive second (3-2) subgroup, 
 the second group comprises subgroups, wherein a lens subgroup in at least said second group moves to (1) bring about a change in a focal length of a whole system and (2) correct an image position for movement in association with a focal length change, and 
 one subgroup in the second group and the third group moves to an image side from a longer working distance (WD) side being a far end toward a shorter working distance side being a near end to correct a focal position for movement in association with a working distance change, and wherein said zoom objective lens for endoscopes satisfies the following conditions:
   0.4<( D 12 t−D 12 w )/ fw≦ 1.077  (1)′
 
   0.02 <ΔDwd/fw< 0.4  (2)
 
   0<( rb+ra )/( rb−ra )<2  (3)
 
   −0.7<1/β wd< 0.2  (4)
 
 
 
       where fw is a focal length of a whole system at the wide-angle end, a figure being obtained in a far end-defining working distance;
 D 12   w  is a spacing between the first group and the second group at the wide-angle end; 
 D 12   t  is a spacing between the first group and the second group at a telephoto end; 
 ΔDwd is an amount of movement of a moving group upon changing of the working distance from a far end to a near end, provided that a plus sign is indicative of a direction of movement of the moving group to an image side; 
 ra is a radius of curvature of an image-side surface of a first lens in the first group; 
 rb is s radius of curvature of an object-side surface of a second lens in the first group; and 
 βwd is an imaging magnification of the moving group upon a working distance change, a figure being obtained at the wide-angle end in a far end-defining working distance. 
 
     
     
       3. The zoom objective lens for endoscopes according to any one of  claims 1  and  2 , characterized in that after ordinary far viewing, the working distance is changed from a longer side to a shorter side for near viewing, and then the focal length of the whole system is changed while the working distance remains fixed for near viewing to implement magnified viewing with higher magnifications. 
     
     
       4. The zoom objective lens for endoscopes according to any one of  claims 1  and  2 , characterized in that:
 the second group moves to the image side from a wide-angle side to a telephoto side, 
 the first (3-1) subgroup of the third group moves in an orbit distinct from that of the second group in such a way as to correct the image position for movement in association with a focal length change, and 
 the first (3-1) subgroup of the third group moves to the image side from a longer side to a shorter side of the working distance (WD). 
 
     
     
       5. The zoom objective lens for endoscopes according to any one of  claims 1  and  2 , characterized in that:
 the first group comprises a negative first (1-1) subgroup and a positive second (1-2) subgroup, 
 the second group moves to the image side from a wide-angle side to a telephoto side, 
 the second (1-2) subgroup of the first group moves in an orbit distinct from that of the second group in such a way as to correct the image position for movement in association with a focal length change, and 
 the first (3-1) subgroup of the third group moves to the image side from a longer side to a shorter side of the working distance (WD). 
 
     
     
       6. The zoom objective lens for endoscopes according to any one of  claims 1  and  2 , characterized in that:
 the first group comprises a negative first (1-1) subgroup and a positive second (1-2) subgroup, 
 from a wide-angle side to a telephoto side, the second (1-2) subgroup of the first group moves to the object side and the second group moves to the image side, 
 the first (3-1) subgroup of the third group moves in an orbit distinct from those of the second (1-2) subgroup of the first group and the second group in such a way as to correct the image position for movement in association with a focal length change, and 
 the first (3-1) subgroup of the third group moves to the image side from a longer side to a shorter side of the working distance (WD). 
 
     
     
       7. The zoom objective lens for endoscopes according to any one of  claims 1  and  2 , characterized in that:
 the first group comprises a negative first (1-1) subgroup and a positive second (1-2) subgroup, 
 the second (1-2) subgroup of the first group moves to the object side from a wide-angle side to a telephoto side, 
 the second group moves in an orbit distinct from that of the second (1-2) subgroup of the first group in such a way as to correct the image position for movement in association with a focal length change, and 
 the second group moves to the image side from a longer side to a shorter side of the working distance (WD). 
 
     
     
       8. The zoom objective lens for endoscopes according to any one of  claims 1  and  2 , characterized in that:
 the second group comprises a negative first (2-1) subgroup and a negative second (2-2) subgroup, 
 from a wide-angle side to a telephoto side, the first (2-1) subgroup of the second group moves to the object side and the second (2-2) subgroup of the second group moves to the image side, 
 the third group moves in an orbit distinct from those of the first (2-1) subgroup of the second group and the second (2-2) subgroup of the second group in such a way as to correct the image position for movement in association with a focal length change, and 
 the second (2-2) subgroup of the second group moves to the image side from a longer side to a shorter side of the working distance (WD). 
 
     
     
       9. The zoom objective lens for endoscopes according to any one of  claims 1  and  2 , characterized in that:
 the second group comprises a positive first (2-1) subgroup and a negative second (2-2) subgroup, 
 the second (2-2) subgroup of the second group moves to the image side from a wide-angle side to a telephoto side, 
 the first (2-1) subgroup of the second group moves in an orbit distinct from that of the second (2-2) subgroup of the second group in such a way as to correct the image position for movement in association with a focal length change, and 
 the second (2-2) subgroup of the second group moves to the image side from a longer side to a shorter side of the working distance (WD).